x700? Oh yea, for sure.
A stronger processer will give you a higher minimum frame rate but it also depends on your monitors max resolution and personal preference. If you only wanna play @ 1024x768, Geforce 7900 series for sure. Past 1280x1028, 8800GTS or 7 series. Any further than 1600x1200 could max your 6300 out. An 8 series is probably overdoing it at 1024x768.
ATi-x1900gt or GF-7900gs/gt. It'l be a able to do that a eat a burger. Maybe step back 1 or 2. 7600gt or 1600gt. 100 - 130 bucks I think. 20/25% slower though. Upcoming games will be a chalenge even @ that resolution. Somewhat of a toss-up cause the 7600 is getting close to your x700 preformance.